1. Field of the Invention
The present invention relates to an encoder, to be attached to a motor or a motor-driven apparatus and to be used for detecting position information or speed information, and to a control apparatus for controlling the motor by receiving and analyzing an analog encoder signal generated within the encoder; more particularly, the invention relates to a technology for providing information useful for the prediction of failure of the encoder.
2. Description of the Related Art
In an encoder attached to a motor or a motor-driven apparatus and used for detecting position information or speed information, failure can occur due to various internal or external factors or due to aging. To cope with the occurrence of such a failure, various techniques have been employed in the prior art, including one such as depicted in the configuration shown in the block diagram of FIG. 1a or 1b which outputs alarm information and notifies the operator accordingly by producing an audible alarm and/or presenting an alarm indication, for example, on a display of a control apparatus.
In the configuration shown in FIG. 1a, an analog sensor signal 11 generated by a detector (not shown) of an optical or magnetic encoder 10 is converted in a block 12 into a digital signal which is supplied to a position/speed detection circuit (“position/speed detection” block 13) and a “characteristic value calculation” block 14. As is well known, the sensor signal 11 contains signals of multiple channels such as two-phase sinusoidal signals (phase A and phase B). The “position/speed detection” block 13 obtains position/speed information based on these signals, and transmits the information to an external control apparatus 20 via a serial data transmit/receive control circuit 16. Based on the transmitted position/speed information, the control apparatus 20 performs feedback control, etc. of the motor (not shown) connected to the control apparatus.
On the other hand, in the “characteristic value calculation” block 14, a characteristic value (for example, the offset value of each phase signal) is calculated repeatedly for each of the two-phase sinusoidal signals at predetermined intervals of time, and the presence or absence of abnormality is checked in an “alarm detection” block 15. For example, an allowable range (from lower limit Vth1 to upper limit Vth2) is set in advance for the offset value, and whether the value is inside the allowable range or not is indicated by outputting a “0” (the value is inside the allowable range) or a “1” (the value is outside the allowable range). This output data is transmitted to the external control apparatus 20 via the serial data transmit/receive control circuit 16. When the “1” signal (the value is outside the allowable range) is transmitted, the control apparatus 20 produces an alarm output and notifies the occurrence of abnormality to the operator by means of a visible and/or audible indication.
In the configuration shown in FIG. 1b, an analog encoder signal 21 containing the two-phase sinusoidal signals generated by a detector of an encoder 10 is transmitted to an external control apparatus 20. In the control apparatus 20, the received signal is A/D converted in a block 22, and position/speed information is obtained based on the A/D converted signal. Then, based on the position/speed information, in a block 26 indicated as “CPU, control means for peripheral circuits, etc.” feedback control, etc. is performed for the motor (not shown) connected to the control apparatus 20.
On the other hand, the A/D converted encoder signal is also supplied to a “characteristic value calculation” block 24 where the characteristic value (for example, the offset value) of the encoder signal is calculated. The characteristic value (for example, the offset value) thus calculated is processed in an “alarm detection” block 25; if it is determined that an abnormality has occurred, an alarm output is produced so as to notify the operator of the occurrence of the abnormality by means of a visible and/or audible indication. The criterion for outputting the alarm is the same as that described with reference to FIG. 1a. That is, for the two-phase sinusoidal signals, for example, the offset value is checked at extremely short predetermined intervals of time (ITP) and, if the offset value is outside the predetermined allowable range (from lower limit Vth1 to upper limit Vth2), the alarm output is produced.
However, with these prior art techniques, it has been difficult to predict failures before outputting the alarm information. Further, according to an empirical rule, there can occur cases where the alarm is produced intermittently, for example, when the allowable range (from lower limit Vth1 to upper limit Vth2) is set relatively narrow, and there have been cases where the cause for it cannot be identified. No literature has been found that describes an effective means for solving such problems.
Accordingly, it is an object of the present invention to solve the above-described problems associated with the prior art. That is, the invention aims to improve an encoder which is attached to a motor or a motor-driven apparatus and used for detecting position information or speed information, or to improve a control apparatus for controlling the motor by receiving and analyzing an analog encoder signal generated within the encoder, and thereby to provide information useful for failure prediction and also information useful for identifying the cause for the intermittent alarm activation. By so doing, the invention also aims to improve the maintainability of the encoder.